1. Field of the Invention
The present invention relates to a portable engine adopted for a portable working apparatus such as a weed cutter.
2. Description of the Prior Art
In a prior art portable engine, an ignition coil for generating an electromotive force is generally fixed to the side face of an engine cylinder through a fitting seat and a tightening bolt. During the operation of engine, heat which is generated in the engine cylinder is transmitted to the ignition coil through the fitting seat and bolt and causes a deterioration in the function of ignition coil. The portable engine is also provided with a fan for cooling the engine cylinder. Air blown from the fan is firstly guided upward by a fan cover fixed to the front side (an output side of the engine) of a crankcase and then toward the periphery of the engine cylinder by a cylinder cover which is formed in series with the fan cover. A partition is provided to cover a step which is formed between the fan cover and the cylinder cover. According to the prior art, this partition is formed integrally with the cylinder cover.
Further, according to the prior art, in positioning the engine cylinder with respect to the crankcase, a lower end of the engine cylinder is fitted to an inner diameter of the crankcase, and the positioning is done in a rotational direction while the engine cylinder is fixed to the crankcase by tightening clamping bolts. In this positioning method, the positioning accuracy may deteriorate due to the tolerance of the clamping bolts and the engaging portion of the crankcase to cause the displacement of a scavenging port and the uneven wear of a piston reciprocating in the engine cylinder. Further, to improve the positioning accuracy, the processing accuracy of the bolts, bolt holes, and the engaging portion of the crankcase must be increased in the prior art so that the number of manufacturing steps and the manufacturing cost is increased.